Zr alloys exhibit irradiation-induced growth and hardening which is associated with the defects and dislocation loops that form during irradiation. In this study, state-of-the-art in-situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM) techniques were used to investigate the stability of dislocation loops in two proton-irradiated Zr-Fe binary alloys in real time. Complementary data from both techniques show rapid annealing of a-loops occurs between 300°C and 450°C. Line profile analysis was performed on the SXRD patterns using the convoluted multiple whole profile analysis tool, to calculate the change in a-loop line density as a function of post-irradiation heat treatment temperature and time. At temperatures below 300°C, no significant decrease in a-loop density was detected when held for one hour at temperature. From this SXRD experiment, we calculate the effective activation energy for the annealing process as 0.46 eV. On-axis in-situ STEM imaging was used to directly observe a-loop mobility during heating cycles and confirm that a-loops begin to glide in the trace of the basal plane at ~200°C in a thin foil specimen. Such a-loop gliding events, leading to annihilation at the foil's surfaces, became more frequent between 300-450°C.
This work represents the first use of proton irradiation to simulate in-core radiation damage in Ti3SiC2 and Ti3AlC2 MAX phases. Irradiation experiments were performed to 0.1 dpa at 350 ˚C, with a damage rate of 4.57 × 10 -6 dpa s -1 . The MAX phases displayed significant dimensional instabilities at the crystal level during irradiation leading to large anisotropic changes in lattice parameter, even at low damage levels. The instabilities were accompanied by a decomposition of the Ti-based MAX phases to their binary constituents, TiC. Experimentally observed changes in lattice parameter have been correlated with density functional theory modelling. The most energetically favourable and/or most difficult to recombine defects considered were an M-A antisite ({MA:AM}), and carbon Frenkel ({VC:Ci}). It is proposed that antisite defects, {MA:AM}, are the main contributor to the observed changes in lattice parameter. The proposed mechanism reported in this work potentially enables to design MAX phase compositions, which do not favour antisite defect accumulation. In addition, comparison between the experimental results and theoretical calculations shows that a greater amount of residual damage remains in Ti3AlC2 when compared to Ti3SiC2 after the same irradiation treatment.
While the evolution of irradiation-induced dislocation loops is well correlated with irradiation-induced growth phenomena, the effect of alloying elements on this evolution remains elusive, especially at low fluences. To develop a more mechanistic understanding of the role of Fe on loop formation, state-of-the-art techniques have been used to study a proton-irradiated Zr-0.1Fe alloy and proton-and neutronirradiated Zircaloy-2. The two alloys have been irradiated with 2 MeV protons up to 7 dpa at 350 °C and Zircaloy-2 up to 14.7 x10 25 n m-2 , ~24 dpa, in a BWR at ~300 °C. Baseline TEM characterisation showed that the Zr 3 Fe secondary phase particles in the binary system are larger and fewer in number than the Zr(Fe, Cr) 2 and Zr 2 (Fe, Ni) particles in Zircaloy-2. Analysis of the irradiated binary alloy revealed only limited dissolution of Ze 3 Fe suggesting little dispersion of Fe into the matrix while at the same time a higher a-loop density is observed in comparison to that in Zircaloy-2 at equivalent proton dose levels. It was also found that the redistribution of Fe during irradiation leads to the formation of Fe nanoclusters. A delay in the onset of c-loop nucleation in proton-irradiated Zircaloy-2 compared to the binary alloy was observed. The effect of Fe redistributed from secondary phase particles, due to dissolution, on the density and morphology of a-and c-loops is described. The implication this may have on irradiation-induced growth of Zr fuel cladding is also discussed.
A. Harte et al., Nano-scale chemical evolution in a proton-and neutron-irradiated Zr alloy J. Nucl. Mater. Accepted Jan. 2017 Nano-scale chemical evolution in a proton-and neutron-irradiated Zr alloy (Fe,Ni). This is accomplished through ultra-high spatial resolution scanning transmission electron microscopy and the use of energy-dispersive X-ray spectroscopic methods. Fe-depletion is observed from both SPP types after irradiation with both irradiative species, but is heterogeneous in the case of Zr(Fe,Cr) 2 , predominantly from the edge region, and homogeneously in the case of Zr 2 (Fe,Ni). Further, there is evidence of a delay in the dissolution of the Zr 2 (Fe,Ni) SPP with respect to the Zr(Fe,Cr) 2 . As such, SPP dissolution results in matrix supersaturation with solute under both irradiative species and proton irradiation is considered well suited to emulate the effects of neutron irradiation in this context. The mechanisms of solute redistribution processes from SPPs and the consequences for irradiation-induced growth phenomena are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.